1. Field of the Invention
The present invention relates to a visibility range measuring apparatus, i.e., apparatus for measuring the range of visibility, for a motor vehicle or the like.
2. Description of Related Art
The visibility range measuring apparatus such as mentioned above is already known, as is disclosed in Japanese Patent Publication No. 75036/1994 (JP-6-75036). The conventional visibility range measuring apparatus includes a light projector or emitter for projecting or emitting light pulses or flashing light and a processing unit for determining or measuring the visibility range by making use of the light undergone back scattering at regions or sections located on an optical path along which the light pulses or flashing light are emitted or projected.
The conventional visibility range measuring apparatus for a motor vehicle however suffers a problem that the visibility range may possibly be measured erroneously due to interference of the light pulses or flashing light emitting from another visibility range measuring apparatus mounted on a motor vehicle traveling, for example, in the opposite direction, because the visibility range measuring apparatus known heretofore is so arranged as to emit light pulses or flashing light for thereby measuring the visibility range on the basis of the reflection or echo light.